Friction twister element

ABSTRACT

Disclosed is an improved friction twisting element for use in a textile yarn false twist spindle. The disclosed friction twisting element, mounted in a false twist spindle capable of rotation about its longitudinal axis, engages a strand of yarn and imparts a plurality of turns of twist to the yarn for each revolution of the spindle. The size and shape of the friction twist element are such that tension fluctuations in the yarn are minimized during the operation of the device. The size and shape of the friction element will also maximize the frictional engagement between the element and the yarn and will avoid yarn slippage that is characteristic of a friction twisting element that has a large variation between the inside and outside diameter of the yarn engaging surface.

United States Patent Richter [4 1 June 13, 1972 FRICTION TWISTER ELEMENT [72] Inventor: Hans l-l. Richter, Warwick, R1.

[73] Assignee: Leesona Corporation, Warwick, R].

[22] Filed: Nov. 16, 1970 [21] App]. No.: 89,552

Related US. Application Data [63] Continuation-impart of Ser. No. 25,559, May 6, 1970.

3,029,591 4/1962 Scragg et al.... ....57/77.4 X 3,066,473 12/1962 Maeda ..57/77.4 3,535,866 10/1970 Tsuruta et al.. .57/77.4 X 3,537,250 1 1/1970 Mackintosh ..57/77.4

FOREIGN PATENTS OR APPLICATIONS Primary Eraminer-Donald E. Watkins Au0rneyShaffert & Miller ABSTRACT Disclosed is an improved friction twisting element for use in a textile yarn false twist spindle. The disclosed friction twisting element, mounted in a false twist spindle capable of rotation about its longitudinal axis, engages a strand of yarn and imparts a plurality of turns of twist to the yarn for each revolution of the spindle. The size and shape of the friction twist element are such that tension fluctuations in the yarn are minimized during the operation of the device. The size and shape of the friction element will also maximize the frictional engagement between the element and the yarn and will avoid yarn slippage that is characteristic of a friction twisting element that has a large variation between the inside and outside diameter of the yarn engaging surface.

19 Claims, 7 Drawing Figures FRICTION TWISTER ELEMENT CROSS REFERENCE TO RELATED APPLICATIONS This application is a continuation-in-part of my US. Pat. application Ser. No. 25,559 entitled, TWISTER AND METHOD OF TWISTING, filed May 6, 1970.

BACKGROUND OF THE INVENTION In recent years, much attention has been given by the textile art to so-called textured synthetic yarns. One such textured synthetic yarn is commonly referred to as a torque stretch yarn." As is well known, these torque stretch yarns have been mechanically treated to assume a crimped and coiled configuration so that they have a certain inherent elasticity and have stretch characteristics that distinguish them from untreated yarns.

A common techniqueemployed in the production of torque stretch yarn, and one that is being practiced on a wide spread scale, is known as false twist texturing. This procedure involves twisting the yarn about its own axis, heat setting the twist, and untwisting the yarn in a continuous operation without interruption between the individual steps.

Numerous devices have been proposed for twisting the yarn about its own axis. Generally, these devices have been mechanical means that are capable of imparting one turn of twist to yarn passing through the device for each turn or rotation of the device itself.

Certain minimum twist concentrations are required to produce commercially acceptable yarn and these minimum concentrations are a function of, among other factors, the denier of the yarn involved. These twist concentrations (usually defined as the number of twists per inch or TPI imparted to the yarn) are required regardless of the lineal speed at which the yarn is processed. The lineal speed at which thermoplastic yarn may be processed is a factor that is desirable to increase if economy of operation is to be improved. As is apparent, an increase in the lineal speed of the yarn will require a device capable of imparting more twists per unit time if the required twist concentration is to be maintained.

Since conventional false twist spindles that impart one turn of twist for one spindle rotation are limited to certain rotational speeds by the strength of conventional materials, there is a definite ceiling on the productivity realized by the use of such devices,

Alternatively, devices have been suggested that will impart more than one turn of twist for each spindle rotation. The name friction twister is often applied to devices of this type. Generally, these devices provide a rotating elastomeric body of a diameter considerably in excess of the diameter of the yarn that is to be twisted. This yarn is passed in contact with this rotating body, frictionally engaged thereby, and, due to the difference in diameter between the body and the yarn, twisted a relatively large number of twists for each rotation of the body. The number of twists imparted to the yarn is, of course, a function of the diameters of the element and the yarn.

An example of such a friction twister is disclosed in US. Pat. No. 3,066,473 to Maeda. This patent discloses a false twisting device having a yarn engaging elastomeric element mounted on the end of a hollow rotating cylinder or spindle.

Several problems have existed with prior art friction twisters. As for example, yarn passing through a hole in the center of a rapidly rotating friction element tends to creep or climb along the inner surface of the element in a direction determined by the direction of rotation of the element itself. The yarn will creep only so far until other influences such as non-uniformity of yarn elongation overcome the frictional forces that cause the yarn to creep. These conditions cause the yarn to fluctuate back and forth across the surface of the friction twisting element which in turn causes uneven wear of the element and undesirable tension fluctuations in the yarn.

Another troublesome problem is attributable to the fact that various points on a rotating body, positioned along a radius taken from the axis of rotation, will have different velocities. Certain types of friction twisters, such as the one in the above mentioned U.S. Pat. No. 3,066,473, are constructed such that the yarn to be twisted passes through a hole formed through the friction element and is then drawn across a large friction surface in the direction of the outer circumference of the element. As such, the yarn contacts a surface that has a wide range of point velocities and, depending on the spacing of the yarn from the axis of rotation, the yarn is twisted varying amounts throughout the extent of its path across the element. This results in extensive slippage between the yarn and the element and twisting efficiency is impaired.

SUMMARY OF THE INVENTION 1 have found that the shape and dimensional relationship of the friction twister yarn engaging element is of importance in maximizing the efficiency of a yarn friction twister.

A toroidal shaped elastomeric element is provided with a given hole diameter and a given outside diameter. The crosssectional shape of the element, taken on a plane containing the longitudinal axis of the element, should be two equal sized circles which, of course, are spaced apart by the hole diameter. The diameter of one of these two circles may be referred to as the minor diameter of the torus or the cross-sectional thickness of the element and the radius of one of these circles may be referred to as the minor radius.

According to the teachings of the present invention, 1 have found that the ratio of the diameter of the hole passing through the element to the cross-sectional thickness should be within the range of 1 to 1 up to 2 to l and preferably in the range of 1.5 to 1 up to 2to 1.

Additionally, the internal diameter or diameter of the hole that passes through the element is an important factor in the control of the tension of yarn being twisted by the element for reasons to be discussed below. I have found that an internal hole diameter of 0.3 (five-sixteenths) inch is quite satisfactory for yarn in the 15 to 70 denier range although some latitude is permitted. The optimum internal diameter is somewhat a function of the denier of the yarn being twisted and a larger denier requires a larger diameter hole.

I have also found that the configuration of the portion of the element surface that is actually contacted by the yarn should be substantially that of an arc of a circle.

Briefly, the dimensions and shape of the friction element may be controlled to maximize the twisting efficiency of the friction element. Controlling the size of the hole or inside diameter is of importance. Increasing the hole diameter will result in an increased number of twists imparted to the strand of yarn for one revolution of the element. Decreasing the hole diameter will result in an increase in the stability of the yarn tension while it is being twisted because the yarn fluctuates over a smaller distance. These two factors must be combined in a manner to obtain the optimum size for the hole diameter.

Controlling the minor diameter or cross-sectional thickness is also of importance. Increasing the minor diameter will result in an increased yarn contacting friction surface on the element which improves the frictional engagement between the yarn and the element. Decreasing the minor diameter will minimize the previously discussed yarn slippage caused by different surface point velocities. Again, both of these factors must be taken into consideration to obtain the optimum minor diameter.

Other factors of the instant invention will be apparent to those skilled in the art from a consideration of this specification, taken in conjunction with the accompanying drawing.

BRIEF DESCRIPTION OF THE DRAWING FIG. 1 is a perspective view of toroidal shaped friction twisting element, mounted on one end of a hollow friction twisting spindle.

FIG. 2 is a schematic elevation of a rotating friction twisting element, showing the configuration that a strand of yarn assumes as it creeps around the inner surface of the element.

FIG. 3 is a schematic drawing of the geometric relationship existent between the yarn path and a friction twisting element of a given internal diameter.

FIG. 4 is a schematic drawing of the geometric relationship existent between the yarn path and a friction twisting element of a given internal diameter less than the diameter of the previous figure.

FIG. 5 is a schematic drawing of the geometric relationship existent between the yarn path and a friction twisting element of a given internal diameter less than the diameter of the previous figure.

FIG. 6 is a schematic drawing of the geometric relationship existent between the yarn path and a friction twisting element of a given internal diameter less than the diameter of the previous figure.

FIG. 7 is a cross-sectional view of the friction twisting element of the instant invention illustrating the manner in which it is mounted in the hollow spindle and the manner in which a strand of yarn is threaded through the twister.

DESCRIPTION OF A PREFERRED EMBODIMENT With particular reference to FIG. 1 friction twisting element 10 is mounted on one end 21 of hollow friction twisting spindle 20. Spindle is a hollow shaft with bore 22 (FIG. 7) passing through the full longitudinal extent thereof. Element engaging groove 23 is formed in the end of spindle 20, circumferentially surrounding bore 22, and complementarily shaped to mate with friction twisting element 10. As can be seen in FIG. 7, the depth of groove 23 when measured inwardly from end surface 24 of spindle 20 is slightly more than the radius of the cross-sectional thickness of portion 10A of friction twisting element 10. Because friction twisting element 10 is made from an elastomeric material with natural resilience and because the depth of the groove exhibits the just discussed dimensional characteristic, friction twisting element 10 may be firmly mounted on the end ofspindle 20 with a simple press fit.

Yarn Y contacts friction twisting element 10 on a portion of its surface that constitutes an arc of a circle. This contact surface is defined as the surface between outer diameter contact point 11 and inner diameter contact point 12. Inner diameter point 12 is the innermost point on the inner surface of the torroidal friction element.

In operation friction twisting element 10 and spindle 20 are rotated about their common longitudinal axis by conventional driving means such as a moving belt in contact with the outer peripheral surface of spindle 20.

With particular reference to FIG. 2 friction twisting element 10 is being rotated in a counter-clockwise direction as indicated by the arrow. The rotary, motion of friction twisting element 10 tends to carry the strand of yarn Y that is in contact with friction twisting element 10 in the direction of rotation of friction twisting element 10. The yarn path is thus distorted or curved in a manner shown in FIG. 2 because the yarn creeps along the inner surface of friction twisting element 10. The yarn itself fluctuates during twisting from a maximum height path indicated with solid lines to a minimum height path indicated with dotted lines.

I have determined that certain advantages and improved twisting efficiencies are attributable to certain characteristics of the size and shape of friction twisting element 10. The most important of these characteristics are the inner diameter of the hole passing through the torroidal shaped element, the ratio of the inner hole diameter to the cross-sectional thickness or minor diameter of the elastomeric element, and the shape of that portion of the surface of the friction twisting element that is actually contacted by the yarn.

Increasing the interior or hole diameter of the element will result in a greater number of twists imparted to the yarn being twisted for each revolution of the element. However, increasing the hole diameter also has an undesirable effect more clearly understood with particular reference to FIGS. 3 to 6.

FIGS. 3 to 6 illustrate the geometric relationships between a strand of yarn while it is being twisted and the inside or hole diameter of the friction twisting element. The distorted or curved path assumed by the yarn during twisting has already been discussed with respect to FIG. 2. It is noted that yarn Y contacts the inner surface of element 10 at point P when the yarn has reached it maximum degree of creep or travel along this surface.

FIGS. 3 to 6 include circles of decreasing diameter, representing the size of the hole through element 10. This circle is indicated in each figure as ID. and the center of the circle or element hole is designated C. Horizontal and vertical axes are indicated by the letters H and V, respectively, and guide point G, representing the center of a yarn guide, is positioned on vertical axis V. The vertical axis intersects the lower side of the circle at point Z and the distance GZ the distance between the guide and the interior surface of the hole remains constant in all four figures.

I have discovered that angle [3 between vertical axis V and line PC, which passes through point P and center C, remains constant independently of the size of the hole or internal diameter of the friction element. Point P represents the point where the yarn contacts the inner portion of the element surface at its maximum height and this point is also illustrated in FIG. 2. The location of point P is a function of the yarn tension, the coefficient of friction of the yarn and the coefficient of friction of the element.

In other words, for any size hole diameter, the maximum position of the yarn path may be determined by constructing a line passing through the geometric center of the hole and forming an angle [3 with the vertical axis V. The apex of angle ,8 coincides with the center of the hole.

In like manner, I have discovered that when other factors such as non-uniformity of elongation begin to affect the yarn as it creeps up the inside element surface, the yarn will drop back to a path illustrated in dotted lines in FIG. 2. Point X represents the point where the yarn contacts the inner portion of the element surface at its minimum height.

A line PG, drawn from point P to point G, forms an angle a with vertical axis V. Because the distance GZ is constant in all figures, the angle a becomes smaller when the diameter of the circle is decreased.

While the locations of X and P demonstrate certain constant angular relationships independent of the hole diameter, the distance PX measured between points P and X is increased as the diameter of the circle or hole increases.

The strand of yarn fluctuates over the surface of the friction element during operation and, when visually observed, can be seen to constantly change paths between the dotted and solid paths shown in FIG. 2.

The yarn is being fed through the friction twister at a constant rate and as distance PG is greater than distance XG, the tension of the yarn changes while the yarn fluctuates. The degree of fluctuation is a function of the distance PX and, of course, distance PX is greater for a hole of larger diameter. Thus, the larger the internal diameter of the element, the greater the distance PX and the greater the undesirable tension variations. As the yarn fluctuates, twist slips through the element and non-uniform yarn is produced. Additionally, the fluctuation causes the yarn to cut or form chatter marks on the surface of the element, necessitating early replacement of the element.

As can be seen in FIGS. 3 to 6, distance PX decreases as the diameter of the hole decreases. It is advantageous to minimize the distance PX thereby to improve the stability of the yarn tension and the quality of the yarn. This minimization of the distance PX and thus the hole diameter must be balanced against the desirability of imparting a plurality of turns of twist to the yarn strand for each turn of the element. The number of turns thus imparted increases as a function of the diameter.

I have found that an interior hole diameter of approximately five-sixteenths inch (0.3125 inch) to twenty-one sixty-fourths inch (0.328 inch) will produce excellent results when the yarn is in a denier range of 15 to 70 denier. Some latitude is allowed but the internal diameter of the hole should not exceed onehalf inch for 15 to 70 denier yarn. As the denier increases, the hole diameter may also be increased. As for example, a 150 denier yarn may be processed with an element having a hole diameter of nine-sixteenths inch (0.5625 inch).

The cross-sectional diameter of circle A or 108 of FIG. 7 may be referred to as either the cross-sectional thickness of the element or the minor diameter of the torroidal shaped element. After the diameter of the hole in the element is determined, it is necessary to determine the optimum shape and size of the elastomeric element itself.

I have determined that the optimum shape for at least that portion of the surface of the element that is contacted by the yarn is an arc of a circle. With specific reference to FIG. 7, this arc may be defined as the portion of the element surface between previously described points 11 and 12. The are may constitute approximately 90 of the full 360 of the circumference of portion 108 of the friction element. As seen in FIG. 7, the yarn path approaches the friction element in a path that forms a small acute angle F with the vertical and departs the friction element substantially parallel with the horizontal. With such a path, the surface contact arc will slightly exceed 90 but the frictional engagement between the yarn and the surface will be improved.

An arc of a circle provides a surface that meets two criteria. First, the yarn engaging surface is smooth and free of sharp edges, both features that improve twisting efficiency. Other surface configurations may be provided that are smooth, but the arch of a circle also exhibits a second advantage. The distance D (FIG. 7), measured between points 12 and 11 in a direction parallel to a radius drawn from the axis of rotation is minimized and consequently the previously discussed point velocity phenomenon is also minimized.

It is desirable to provide a friction surface that will be of such a size to insure good frictional engagement between the surface and the yarn yet will avoid large point velocity differences, as the latter causes undesirable yarn slippage. An arc of a circle provides such a surface.

While the friction surface need only present an arc of a circle to the yarn, it is more convenient to provide the torus or O- ring shaped friction element disclosed herein. As for example, when wear occurs on the surface of the torroidal element, it is only necessary to remove it from element engaging groove 23 and reverse its position in order to provide a new twisting surface for the yarn.

Once the shape of the element has been determined, it is only necessary to determine the minor diameter or cross sectional thickness of the element.

I have found that a relationship exists between the size of the hole diameter and the size of the minor diameter. This relationships may be expressed as the ratio of internal diameter to cross-sectional thickness and should be in the order of l to 1 up to 2 to l. Preferably, the ratio should be within the range of 1.5 to 1 up to 2 to l.

l have found that, for example, with a hole diameter of 0.328 inch, excellent yarn may be produced with an element that has a minor diameter of 0.187 inch. The ratio of 0.328 to 0.187 is approximately 1.75 to l. A torus shaped friction element with these dimensions, when used to twist yarn, provides excellent results with yarn in the 15 to 70 denier range. If larger denier yarns are used, a large hole diameter may be employed that has a correspondingly larger minor diameter, both still in a ratio of approximately 1.75 to l for optimum results.

The elastomeric material best suited for the friction twisting element disclosed herein has a high coefficient of friction and a wear resistant surface. An example of such a material is polyurethane and a friction element of this material should have a Durometer hardness of approximately 50-60 on the A scale.

With particular reference to FIG. 7, it is noted that the yarn path of the yarn to be twisted contacts an are slightly in excess of As discussed above, the actual yarn path approaches the element and forms an angle F with the vertical or with a yarn path that would contact only 90 of the surface of the element, assuming that the yarn departs the element parallel to the horizontal. Thus, the actual arc of contact would be 90 plus the value of angle F. This increased contact improves the frictional engagement between the yarn and the surface. Of course, a similar relationship would exist if the yarn contacted less than 90 of the element surface although twisting efficiency would be somewhat impaired. Such a situation would exist if, for example, the yarn path approached the element in a path slightly to the left of the vertical (FIG. 7) or departed in a path slightly above the horizontal. In these instances, the are contacted by the yarn would be 90 minus the angle defined between the actual path of the yarn to be twisted and a yarn path contacting only 90 of the element surface when the actual path contacts less than 90 of said are. In this discussion, the yarn has been defined as approaching" and departing" the element in the direction shown by the arrow in FIG. 7. It is understood that the yarn may actually move in either direction during the twisting operation.

Although the above mentioned ratios have been discussed in terms of the minor diameter, it should be noted that the minor radius may also be employed to calculate a different but equivalent ratio. With particular reference to FIG. 7, it is noted that mid-line M is drawn across the surface of the cross section of element section 10B. The portion of section 108 that is to the right of line M actually provides no yarn engaging surface, although it is employed to grip the spindle groove 23. As is apparent, the mounting arrangement of the spindle could be modified so that a portion of the toroidal-shaped element could be eliminated.

Minor radius r (FIG. 7) may be employed to calculate a ratio defined as the ratio of the diameter of the hole passing through the toroidal-shaped element to the minor radius of the toroidal-shaped element. Where the previously discussed ratio that used the minor diameter had an optimum valve of approximately 1.75 to l, the ratio employing the minor radius would be approximately 3.5 to l or simply double the minor diameter ratio.

Thus the ratios discussed in this disclosure may employ either the minor diameter of the toroidal-shaped element or the minor radius of an element that is at least a portion of a torus which presents a yarn engaging surface shaped, in cross section, as an arc of a circle.

It should be understood that the present invention may be embodied in other specific forms without departing from the spirit or essential attributes thereof, all of which are intended to be encompassed by the appended claims.

I claim:

1. In a textile yarn false twist friction twisting device including hollow spindle means mounted for rotation about its longitudinal axis and friction twisting element means on said spindle means, the improvement comprising yarn engaging surface means on said element means configured in cross section as an arc of a circle, said surface means being at least a portion of a surface of a torus, and wherein the diameter of the hole passing through said torus is in the ratio of 2 to 1 up to 4 to l to the minor radius of said torus.

2. The improvement of claim 1 wherein said ratio is in the rangeof3tolupto4tol. 1

3. The improvement of claim I wherein said ratio is approximately 3.5 to l.

4. In a textile yarn false twist friction twisting device including hollow spindle means mounted for rotation about its longitudinal axis and friction twisting element means on said spindle means, the improvement comprising said friction twisting element being in the shape of a torus and wherein the diameter of the hole passing through said torus is in the ratio of l to 1 up to 2 to 1 to the minor diameter of said torus.

5. The improvement of claim 4 wherein said ratio is in the range of 1.5 to l upto2to 1.

6. The improvement of claim 4 wherein said ratio is approximately 1.75 to l.

7. A friction twisting element for use in a textile yarn false twist friction twisting device comprising a toroidal element adapted to be mounted for rotation about its longitudinal axis, wherein the diameter of the hole passing through said toroidal element is in the ratio of l to 1 up to 2 to 1 to the minor diameter of said toroidal element.

8. A friction twisting element according to claim 7 wherein said ratio is in the range of 1.5 to 1 up to 2 to 1.

9. A friction twisting element according to claim 7 wherein said ratio is approximately 1.75 to l.

10. A friction twisting element for use in a textile yarn false twist friction twisting device comprising a hollow friction twisting spindle having an inner surface defining a longitudinal bore therein, a toroidal element mounted at one end of said spindle, a groove being formed at the one end of said spindle and complementarily shaped to mate with said toroidal element such that the depth of said groove when measured inwardly is slightly more than the radius of the cross-sectional thickness of said toroidal element adjacent the one end of said spindle and the inside diameter of said toroidal element is less than the diameter of said inner surface of said spindle, and a portion of the surface of said toroidal element presents a yarn engaging surface that is configured in cross section as an arc of a circle, wherein said are of a circle is approximately a 90 arc plus an angle defined between the actual path of the yarn to be twisted and a yarn path contacting only 90 of said yarn engaging surface when said actual path contacts more than 90 of said surface.

11. A friction twisting element for use in a textile yarn false twist friction twisting device comprising a hollow friction twisting spindle having an inner surface defining a longitudinal bore therein, a toroidal element mounted at one end of said spindle, a groove being formed at the one end of said spindle and complementarily shaped to mate with said toroidal element such that the depth of said groove when measured inwardly is slightly more than the radius of the cross-sectional thickness of said toroidal element adjacent the one end of said spindle and the inside diameter of said toroidal element is less than the diameter of said inner surface of said spindle, and a portion of the surface of said toroidal element presents a yarn engaging surface that is configured in cross section as an arc of a circle, wherein said are of a circle is approximately a 90 arc minus an angle defined between the actual path of the yarn to be twisted and a yarn path contacting only of said yarn engaging surface when said actual path contacts less than 90 of said surface.

12. A friction twisting element according to claim 7 wherein said element is a polyurethane element.

13. A friction twisting element according to claim 12 wherein said polyurethane element has a Durometer hardness in the range of approximately 50 to 60 on the A scale.

14. A friction twisting element for use in a textile yarn false twist friction twisting device comprising yarn engaging surface means on said element configured in cross section as an arc of a circle, said surface means being at least a portion of a surface of a torus, and wherein the diameter of the hole passing through said torus is in the ratio of 2 to 1 up to 4 to 1 to the minor radius of said torus.

15. A friction twisting element according to claim 14 wherein said ratio is in the range of 3 to 1 up to 4 to 1.

16. A friction twisting element according to claim 14 wherein said ratio is approximately 3.5 to 1.

17. A method for false twist texturing of untreated textile yarn comprising the steps of rotating a hollow spindle about its longitudinal axis, said hollow spindle having a toroidal friction twisting element mounted at one end thereof;

feeding untreated textile yarn from a supply source to a portion of the surface of said toroidal element constituting a yarn engaging surface configured in cross-section as an arc of a circle; passing the yarn over said yarn engaging surface such that said arc of a circle is approximately a 90 arc plus an angle defined between the actual path of the yarn to be twisted and a yarn path contacting only 90 of said yarn engaging surface so that the actual path of the yarn contacts more than 90 of said yarn engaging surface; and thereafter passing the yarn through said hollow spindle.

18. A method in accordance with claim 17, wherein the yarn path to said yarn engaging surface which contacts only 90 of said surface is perpendicular to the yarn departing from said yarn engaging surface.

19. A method in accordance with claim 18, wherein the yarn departing from said yarn engaging surface is passed through said hollow spindle substantially parallel to the longitudinal axis of said spindle. 

1. In a textile yarn false twist friction twisting device including hollow spindle means mounted for rotation about its longitudinal axis and friction twisting element means on said spindle means, the improvement comprising yarn engaging surface means on said element means configured in cross section as an arc of a circle, said surface means being at least a portion of a surface of a torus, and wherein the diameter of the hole passing through said torus is in the ratio of 2 to 1 up to 4 to 1 to the minor radius of said torus.
 2. The improvement of claim 1 wherein said ratio is in the range of 3 to 1 up to 4 to
 1. 3. The improvement of claim 1 wherein said ratio is approximately 3.5 to
 1. 4. In a textile yarn false twist friction twisting device including hollow spindle means mounted for rotation about its longitudinal axis and friction twisting element means on said spindle means, the improvement comprising said friction twisting element being in the shape of a torus and wherein the diameter of the hole passing through said torus is in the ratio of 1 to 1 up to 2 to 1 to the minor diameter of said torus.
 5. The improvement of claim 4 wherein said ratio is in the range of 1.5 to 1 up to 2 to
 1. 6. The improvement of claim 4 wherein said ratio is approximately 1.75 to
 1. 7. A friction twisting element for use in a textile yarn false twist friction twisting device comprising a toroidal element adapted to be mounted for rotation about its longitudinal axis, wherein the diameter of the hole passing through said toroidal element is in the ratio of 1 to 1 up to 2 to 1 to the minor diameter of said toroidal element.
 8. A friction twisting element according to claim 7 wherein said ratio is in the range of 1.5 to 1 up to 2 to
 1. 9. A friction twisting element according to claim 7 wherein said ratio is approximately 1.75 to
 1. 10. A friction twisting element for use in a textile yarn false twist friction twisting device comprising a hollow friction twisting spindle having an inner surface defining a longitudinal bore therein, a toroidal element mounted at one end of said spindle, a groove being formed at the one end of said spindle and complementarily shaped to mate with said toroidal element such That the depth of said groove when measured inwardly is slightly more than the radius of the cross-sectional thickness of said toroidal element adjacent the one end of said spindle and the inside diameter of said toroidal element is less than the diameter of said inner surface of said spindle, and a portion of the surface of said toroidal element presents a yarn engaging surface that is configured in cross section as an arc of a circle, wherein said arc of a circle is approximately a 90* arc plus an angle defined between the actual path of the yarn to be twisted and a yarn path contacting only 90* of said yarn engaging surface when said actual path contacts more than 90* of said surface.
 11. A friction twisting element for use in a textile yarn false twist friction twisting device comprising a hollow friction twisting spindle having an inner surface defining a longitudinal bore therein, a toroidal element mounted at one end of said spindle, a groove being formed at the one end of said spindle and complementarily shaped to mate with said toroidal element such that the depth of said groove when measured inwardly is slightly more than the radius of the cross-sectional thickness of said toroidal element adjacent the one end of said spindle and the inside diameter of said toroidal element is less than the diameter of said inner surface of said spindle, and a portion of the surface of said toroidal element presents a yarn engaging surface that is configured in cross section as an arc of a circle, wherein said arc of a circle is approximately a 90* arc minus an angle defined between the actual path of the yarn to be twisted and a yarn path contacting only 90* of said yarn engaging surface when said actual path contacts less than 90* of said surface.
 12. A friction twisting element according to claim 7 wherein said element is a polyurethane element.
 13. A friction twisting element according to claim 12 wherein said polyurethane element has a Durometer hardness in the range of approximately 50 to 60 on the A scale.
 14. A friction twisting element for use in a textile yarn false twist friction twisting device comprising yarn engaging surface means on said element configured in cross section as an arc of a circle, said surface means being at least a portion of a surface of a torus, and wherein the diameter of the hole passing through said torus is in the ratio of 2 to 1 up to 4 to 1 to the minor radius of said torus.
 15. A friction twisting element according to claim 14 wherein said ratio is in the range of 3 to 1 up to 4 to
 1. 16. A friction twisting element according to claim 14 wherein said ratio is approximately 3.5 to
 1. 17. A method for false twist texturing of untreated textile yarn comprising the steps of rotating a hollow spindle about its longitudinal axis, said hollow spindle having a toroidal friction twisting element mounted at one end thereof; feeding untreated textile yarn from a supply source to a portion of the surface of said toroidal element constituting a yarn engaging surface configured in cross-section as an arc of a circle; passing the yarn over said yarn engaging surface such that said arc of a circle is approximately a 90* arc plus an angle defined between the actual path of the yarn to be twisted and a yarn path contacting only 90* of said yarn engaging surface so that the actual path of the yarn contacts more than 90* of said yarn engaging surface; and thereafter passing the yarn through said hollow spindle.
 18. A method in accordance with claim 17, wherein the yarn path to said yarn engaging surface which contacts only 90* of said surface is perpendicular to the yarn departing from said yarn engaging surface.
 19. A method in accordance with claim 18, wherein the yarn departing from said yarn engaging surface is passed through said hollow spinDle substantially parallel to the longitudinal axis of said spindle. 